depthcharge: store vb2_context and allocate vboot workbuf

depthcharge should own vb2_context for communicating with vboot.

workbuf should be allocated by depthcharge and pre-filled with
incoming data from coreboot.

BUG=b:124141368, chromium:951692
TEST=Flash and test on eve
CQ-DEPEND=CL:1560716
BRANCH=none

Change-Id: Ibbc22695df254134b5d6c3da1efb72494346f35c
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1563872
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
3 files changed